I. V. Kalchuk and Y. I. Kharkevych, “Approximation of (ψ, β)-differentiable functions by Weierstrass integrals”, Ukr. Mat. Zhurn., vol. 59, no. 7, pp. 953–978, Jul. 2007, Accessed: Dec. 15, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3359